Mechanical Seal Heat Checking Solutions for SAGD Operations
by Thomas Webster, on Thu, Jun 24, 2021 @ 08:06 AM
Mechanical seal heat checking is characterized by the presence of radial cracks originating from the center of metallic, tungsten carbide, or ceramic seal faces. This may appear as scoring or a checkered pattern to the naked eye but is typically fine cracks in the seal face. Heat checking cracks are the result of the combination of the mechanical load (friction and pressure) on seal faces and thermal heating.
When operations are running smoothly, mechanical seal heat checking may go unnoticed until it is too late to salvage the seal. In steam-assisted gravity drainage (SAGD) applications, heat checking may be a more prevalent problem in rotating equipment due to the high temperatures and high viscosity fluids associated with SAGD.
Failure to proactively assess seal faces for heat checking may result in:
- Mechanical seal leakage
- Seal face damage resulting in shorten seal life
- Mechanical seal failure
- Rotating equipment component damage
Below, we will detail common reasons for mechanical seal heat checking and potential solutions for SAGD operations.
Why Mechanical Seal Heat Checking Occurs in SAGD
Heat checking may occur as the result of insufficient lubrication of seal faces or inadequate cooling/inability to maintain the temperature in the seal chamber.
Insufficient Lubrication of Seal Faces
Insufficient lubrication is a common cause of mechanical seal heating checking in SAGD applications. Seal faces may experience insufficient lubrication as a result of:
- Changes in buffer/barrier fluid properties as seasonal temperature changes occur
- Incorrect selection of buffer/barrier fluid
- Buffer/barrier fluids not compatible with the process fluid
- Dry pump startups
- Elevated pressure between seal faces
- Excessive diffusion of process fluid into buffer/barrier fluid
Changes in Buffer/Barrier Fluid Properties
As temperatures change throughout the year, buffer/barrier fluids’ properties are likely to change as well. For example, a buffer/barrier fluid may operate smoothly during spring, summer, and fall months, providing adequate flow to properly lubricate seal faces. However, the viscosity of the fluid increases with cold winter temperatures, resulting in reduced flow and thus, insufficient lubrication.
Incorrect Selection of Buffer/Barrier Fluids
Incorrect selection of buffer/barrier fluids is the most common reason for mechanical seal heat checking. This comes down to having a buffer/barrier fluid with the correct viscosity for a given SAGD process. If fluid viscosity is too high, flow rates may be too low to provide the amount of lubrication and flush needed for mechanical seals to properly operate. Inadequate lubrication can result in excessive friction and consequently, heat checking on seal faces.
Dry Pump Startups
Dry pump startups may occur as a result of unexpected reduction or lack of flush fluid flow. This may be caused by an issue with the seal flush system or a kink in tubing. Lack of flush fluid flow can cause severe heat checking due to elevated frictional loads and excessive heat buildup.
Elevated Pressure Between Seal Faces
Pressure buildup between seal faces that exceed the design specifications of seal face materials can prevent adequate flow of buffer/barrier fluids, resulting in poor lubrication of seal faces.
Excessive Diffusion of Process Fluid into Buffer/Barrier Fluid
SAGD applications can be inherently challenging due to the heavy, viscous crude oils that are pumped. In some cases, the buffer/barrier fluid may be chemically compatible with the process fluid, yet still experience lubrication issues. When heavy crude oil mixes with buffer/barrier fluids, the viscosity can increase significantly, reducing the flow rate and thus, reducing lubrication to seal faces.
Inadequate Cooling or Inability to Maintain Seal Chamber Temperature
When seal flush systems are unable to provide the necessary cooling to mechanical seal faces, heat checking may occur. Inadequate cooling may be the result of:
- Incorrect selection of buffer/barrier fluid resulting in reduced flow rates and increased heat buildup
- Vapourization at seal faces caused by inadequate heat removal resulting in fluid flashing or rapid evaporation
- Disrupted fluid flush resulting from a blockage in tubing or filters
- Scaling on heat exchanger coils resulting in decreased heat removal capabilities
- Changes in process conditions leading to increased process fluid temperatures that exceed the specifications of mechanical seals or seal flush systems
Mechanical Seal Heat Checking Solutions
The best way to prevent heat checking is to take proactive measures to ensure proper lubrication and cooling of seal faces and regularly evaluate how changes in process conditions might be affecting mechanical seals. However, if heat checking is caught early, mechanical seals can potentially be salvaged.
Below, we have detailed how to evaluate mechanical seals and seal flush systems to determine the cause of heat checking and remedy the issue:
Look to Seal Flush System Experts
When heat checking is present, it can be challenging to determine the root cause and best course of action. Mechanical seal vendors and seal flush system experts should be consulted to determine how to remedy heat check issues, whether that be to:
- Replace mechanical seals that are outdated or cannot support harsh process conditions
- Determine the correct buffer/barrier fluid
- Modify, upgrade, or replace seal flush systems to provide better lubrication and cooling to seal faces
At Edmonton Valve & Fitting, we understand the importance of providing mechanical seals with proper lubrication and cooling to minimize heat checking-related downtime in SAGD operations. Our Field Advisors can provide onsite consultations to determine the appropriate seal flush plan equipped with proper instrumentation and components to reduce the likelihood of heat checking.